[Chops]

Quote:

Originally Posted by Kipper /img/forum/go_quote.gif how much were the parts so far? keep it up!!

$40 for the Mundorf caps
$20 for the Hovland caps
$18 for the ALPS 100k
$30 for the driver tube and output tubes
$160 for the amp

A couple more things I'm going to do is replace the power switch and headphone jack, upgrade some of the resistors, probably with some Rikens or Audio Note Tantalums, and wire the output of the Mundorfs directly to the new headphone jack.

In fact, I'm getting just the slightest bit of 60Hz hum coming through with the volume set between 12 through 4 o'clock positions. I never go over 11 o'clock, but just the fact of knowing that it's there bothers me. So tomorrow, I'm going to connect a ground wire from the a/c connector to the chassis to see if that helps.

 

[dcheming]

"In fact, I'm getting just the slightest bit of 60Hz hum"

Have you grounded the body of the ALPS pot yet? The stock carbon pot had a little jumper soldered from the ground pins to the body of the pot itself to prevent hum. When I put in the ALPS I had pretty bad hum so I just grounded the circuit ground to the chassis at one of the stand-offs and that completely removed it. I don't know if it's necessary to ground the chassis itself to earth and doing so might cause ground loops with your source.

 

[Chops]

Quote:

Originally Posted by dcheming /img/forum/go_quote.gif "In fact, I'm getting just the slightest bit of 60Hz hum" Have you grounded the body of the ALPS pot yet? The stock carbon pot had a little jumper soldered from the ground pins to the body of the pot itself to prevent hum. When I put in the ALPS I had pretty bad hum so I just grounded the circuit ground to the chassis at one of the stand-offs and that completely removed it. I don't know if it's necessary to ground the chassis itself to earth and doing so might cause ground loops with your source.

Hey Derek,

Looks like you just saved me a hassle, with the groud loops and all that is.

So from looking at the pic below, all I have to do is connect a ground wire from the copper jumper on the pot to the chassis? That should be simple enough. Thanks again as usual!

 

[Chops]

Alright, so first thing this morning, I scraped off a little paint on the very edge of the chassis right along side the ALPS, took a screwdriver, shorted it to the chassis and the jumper on the pot. I then slowly turned the volume up all the way to max, and guess what?... No more hum!

Once again Derek, you were right.

So the ole' smoldering iron came out once again. I found an old ground wire with the lug already soldered on, cut it to length, scraped the paint off around one of the screws for the front panel, screwed the lug on there, tinned and soldered the other end to the jumper wire on the pot, and that was that.

And of course, I have pics!

 

[Chops]

Well, I'm trying something else now with this amp. Now I know that drarthurwells did a bunch of research on tubes for this amp, but there were a couple I wanted to try on my own. Maybe they might turn out pretty decent.

Let me know what you think...

First up, a pair of Amperex-Japan 6DJ8/E88CC tubes.

And a single NOS GE JAN 5670 tube.

IIRC, I read somewhere within drarthurwells' 708B thread that the GE 5670 tube had some hum or noise or something. Of course, this was with a bone stock 708B. Since I've done a few mods to my amp, things might be different with this tube.

As far as the Amperex 6DJ8s, I don't know if anyone has tried these or not. I can't remember if drarthurwells said anything about these. But all 3 tubes were cheap enough I thought, so I figured why not try them. If worse comes to worse, I'll just turn around and resell them.

 

[Chops]

BTW, I think those Amperex tubes might be Matsu****a's. If that's the case, these are supposed to be pretty decent tubes. At least, that's what I read somewhere on the forum.

 

[Chops]

Also just put in another order with PC...


Input/Output:

TANTALM - 62762 10R 2 watt $12.95 x2
TANTALM - 62712 1K 1/2 watt $4.75 x2



PS:

DIODES - 56739 Vishay-Telefunken SF4007 $0.35 x2



Anode Resistors:

KIWAME- 66220 33K 2 Watt $1.05 x2



The rest:

PRP - 50324 1K0 1 Watt $0.65 x2
PRP - 64726 1M0 0.5 Watt $0.45 x4
PRP - 70164 200R 0.5 Watt $0.45 x2
PRP - 62501 220R 1 Watt $0.65 x2
PRP - 50094 100R 0.5 Watt $0.45 x4

 

[Chops]

When I got home from work today, not only did I find that my new NOS GE JAN 5670 driver tube had arrived, but also the NOS Amperex 6DJ8 output tubes as well!

Now I've read a few horror stories about the GE JAN 5670 creating some noise and/or hum in the 708B amp. This may be so with one in stock form, but mine if far from being stock, and from the list in my previous post above, it's going to be that much further from stock.

Anyway, back to the point. I've had these tubes up and running for the past 5 hours, and they are all completely and 100% silent throughout the entire volume range. This amp is about as "black" as you can get.

As for the sound... Well, with only a few hours on these new tubes, I feel that they have a better "grip" on the music than the previous set that drarthurwells recommended. They DO have a wider soundstage, the dynamics are more dynamic, bass seems to be a bit tighter, the midrange is definately smoother, and the treble is still smooth, crisp and extended.

I'll go a little deeper into the sound of these tubes once I get a good amount of hours on them, but things seem to be better so far. I imaging they can only get better with time.

Now for a few more pics...

Out with the old.

In with the new.

Here they are juiced up.

And a nice close-up of them at work.

 

[Chops]

Hey, I got an unexpected package this morning from FedEx (at least not this soon). I thought for sure this was coming a few days later, and not as one package. Cool!

Here's a break-down of the new components...

1) Vishay-Telefunken Ultrafast Soft Recovery Diodes

2) Audio Note Tantalum I/O resistors

3) KIWAME Anode Load resistors

4) PRP various resistors to replace all the others

I'm hoping that after replacing all of these components, that this amp will really transform into something special.

And here are two (actually four) upgraded opamps for the brand new Music Hall CD25.2 cdp that I will be receiving tomorrow sometime. These are the Burr Brown OPA-627 Opamps to replace the stock (only two) inexpensive 2604 opamps. Obviously, I'll give the stock cdp a good listen before I pop in these new opamps. The Burr Brown upgrade is supposed to provide "additional warmth I wanted, but also deeper, more incisive bass; and a deeper, wider, taller soundstage with increased dynamics. The most significant but unexpected improvement is that each voice and instrument is now full, rich, three-dimensional, and temporally correct." - As per one of the many owner feedbacks on Underwood HiFi's site.

Walter is a great guy who knows how to treat his customers, even a new customer like me! He cut me an extremely excellent deal on the Music Hall, hence the reason I was able to go ahead with the opamp upgrade as well! Fine times are-a comin'.